pnfs-obj: move to ore 02: move to ORE

pnfs-obj: move to ore 02: move to ORE

In this patch we are actually moving to the ORE.
(Object Raid Engine).

objio_state holds a pointer to an ore_io_state. Once
we have an ore_io_state at hand we can call the ore
for reading/writing. We register on the done path
to kick off the nfs io_done mechanism.

Again for Ease of reviewing the old code is "#if 0"
but is not removed so the diff command works better.
The old code will be removed in the next patch.

fs/exofs/Kconfig::ORE is modified to also be auto-included
if PNFS_OBJLAYOUT is set. Since we now depend on ORE.
(See comments in fs/exofs/Kconfig)

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>